The intriguing substitution behavior of CO with bidentate phosphine ligands induced by a gem-dialkyl effect

The reaction of the complexes [FeCpX(CO)2] (X = Cl, Br, I) into either [FeCp(CO)(PP)]X or [FeCpX(PP)] (PP = a bidentate diphosphine ligand) is shown to be highly dependent of the phosphine ligand used. Diphosphine ligands that form stable chelates favor formation of the neutral complex, whereas diphosphine ligands that form less stable chelates favor formation of the cationic complex. Thus, with the use of dppdmp (= 1,3-bis(diphenylphosphino)-2,2-dimethylpropane) the [FeCpX(PP)] complexes (X = Cl, Br, I) are selectively formed, induced by a gem-dialkyl effect. Apart from the bidentate phosphine ligand, the halide ion present in the iron complex has a significant influence on the course of the substitution reaction.

Graphical abstractThe substitution behavior of the compound [FeCpX(CO)2] with bidentate phosphine ligands is determined by the nature of the ligand and the halide ion present on the Fe(II) complex. A gem-dialkyl effect induces the concerted substitution of two CO ligands to form [FeCpX(PP)] complexes.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Reaction of the complex [FeCpX(CO)2] is shown to be dependent on the ligand used. ► Diphosphines that form stable chelates form the neutral complex [FeCpX(PP)] ► Ligands that form less stable chelates form the cationic complex [FeCp(CO)(PP)]X ► The halide ion X also has an influence on the course of the substitution reaction.